This invention relates to a semiconductor device. In particular, this invention relates to a semiconductor device having a semiconductor substrate including an AlGaN layer on a GaN layer.
In recent years, GaN High Electron Mobility Transistor (HEMT) devices have drawn a lot of attention regarding their high potential to replace Si or SiC for use as High Voltage (HV) devices. GaN HEMTs are typically fabricated by applying ohmic source and drain contacts and a Schottky gate contact on top of an epitaxially grown structure including an AlGaN barrier layer on a GaN channel layer.
As AlGaN is a piezoelectric material, the lattice mismatch between GaN layer and the AlGaN layer gives rise to a potential difference over the barrier, which modulates the band structure in such a way that a quantum well filled by two dimensional electron gas spontaneously forms in the GaN near the AlGaN/GaN interface. The high mobility of this electron gas leads to devices having very low resistance compared to other kinds of Field Effect Transistor (FET). As with other FETs, the conductivity in the channel can be modulated by the application of a potential to the gate.
GaN HEMT devices find application as RF power devices in areas where high gain and low noise are required at high frequency. They offer the advantages of higher efficiencies, larger bandwidth and larger temperature range over Si LDMOS and of higher polarization voltage over GaAs HEMT devices. Moreover, GaN HEMT devices start to penetrate e.g. the power conversion market in the voltage range from 50V to 600V, where the GaN devices offer very low specific on-resistances compared to Si based contenders and at lower prices than the competing wide-band-gap material SiC devices.